1. Field of the Invention
The present invention relates to a data processing apparatus, and more particularly to a communication process for information data.
2. Related Background Art
Recently equipment for recording digital image data of a moving image or a still image, such as a digital camera or a digital video camera, is becoming popular.
In the digital camera, a compact memory card is widely employed as the recording medium, and there is also available the camera of a type capable of recording moving image data in addition to still image data.
In the digital video camera, a magnetic tape is widely employed as the recording medium. In addition, there is also available the camera of a type utilizing a recording medium capable of random access such as a compact memory card or a magnetooptical disk, thereby being capable of recording not only moving image data but also still image data. The digital video camera utilizing such random accessible recording medium is arranged to store the image data in a file format.
In such equipment, transferring image data through a cable connected to another equipment is commonly practiced, and in particular, a data transfer format called IEEE 1394 interface is widely utilized in the digital video camera.
The IEEE 1394 interface is featured by including, as the transfer modes, an asynchronous transfer mode (non-synchronized transfer mode) for transferring non-synchronized data, and an isochronous transfer mode (synchronized transfer mode) for transferring synchronized data such as real-time video stream data.
The isochronous transfer mode is effective for transferring data a predetermined data amount of which is required to be transferred continuously at a constant transfer rate, such as moving image stream data. For example, in case of connecting a digital video camera and a personal computer (PC) through an IEEE 1394 interface, it is made possible, by utilizing the isochronous transfer mode, to cause the PC to decode the image data transferred from the digital video camera to the PC and to display such image data on real-time basis on a monitor of the PC.
On the other hand, the asynchronous transfer mode is effective for transferring data that is required to be transferred to a designated node in non-synchronous manner, for example a control command or file data. Also in the asynchronous transfer mode, there can be made a response indicating that a receiving operation has been executed, so that the communication can be executed more securely than in the isochronous transfer mode. In case of transmitting or receiving the image data by the digital video camera on real-time basis utilizing the IEEE 1394 interface, it is common to utilize the isochronous transfer mode. Also the asynchronous transfer mode is incapable of ensuring transfer of moving image data or the like at a predetermined timing, and is therefore unsuitable for the transfer of data which may be required to be decoded and monitored in the course of reception thereof, such as moving image stream data.
For example, there is widely available an application software which, in case of connecting a digital video camera and a PC through an IEEE 1394 interface, attains that the PC decodes the image data transmitted from the digital video camera to the PC by the isochronous transfer mode, to be displayed in real-time. There is also available an application software which attains to store the image data transmitted to the PC in the isochronous transfer mode, in a hard disk of the PC in response to a user instruction thereby preparing a moving image data file.
It is also commonly executed to connect two digital video cameras with an IEEE 1394 interface to execute a dubbing of the image data utilizing the isochronous transfer mode.
However, in case of recording an image data stream transferred in the real-time transfer mode, onto a recording medium, there remains a possibility, as a problem, that the image data stored in the recording medium of the equipment at the transmitting side do not completely coincide with the image data recorded in the equipment of the image receiving side.
For example, in case of connecting a digital video camera which handles the image data on the recording medium as an image data file, with a PC through an IEEE 1394 and storing as a file in the PC the image data transmiferred from the video camera in the isochronous mode, the PC initiates the recording of the image data from a position where the start of recording is instructed, so that the moving image data may not completely coincide in a start portion or an end portion of such moving image data between recording medium and the PC.
As a result, the image data file recorded in the PC becomes different from the original image data file present on the recording medium of the digital video camera.
Also, the isochronous transfer mode, which has a real-time property, is suitable for transferring data which include time-related information such as moving image data or audio data, but is unsuitable for transferring still image data.
In case of transferring still image data in the isochronous transfer mode, the transfer has to be executed after such still image data is converted into a format corresponding to moving image data. For this reason, the receiving side receives image data which is different from the original image data.
Also, even in case of transferring moving image data, the image data format that can be transferred in the isochronous transfer mode is limited in certain equipment, so that there is anticipated a situation where the image data to be transferred has to be converted into a transferrable format before the transmission can be made.
As explained in the foregoing, in case of transmitting the image data as a continuous stream by a real-time transfer method such as the isochronous transfer mode,-there results in a possibility that the transferred image data are different from the original image data. Such possibility is not limited to the case of connecting the digital video camera and the PC but may appear in all the image data exchange utilizing the real-time transfer method.
Also in case of receiving and storing the image data utilizing the real-time transfer method, the stored image data file becomes different from the original image data file. Such storage of image data file may be different from what is intended by the user, and may cause a confusion.